1. Field of Invention
The present invention relates to an apparatus for controlling a liquid crystal timing. More particularly, the present invention relates to an apparatus for controlling a liquid crystal timing, in which a back light driving device is built-in.
2. Description of Related Art
The liquid crystal display (LCD) has had applications on the calculator and the electronic watches since 1970. After then, many properties of photoelectric effect have been discovered, and the driving technologies have been greatly improved. Now, the LCD has several advantages, such as high quality of image displaying, low power consumption, thin and in massive production, low driving voltage, and small volume. The current applications have been applied to the portable TV, image phone, video device, notebook computer, desk displaying terminal, or the projection color TV. It have been one of the promising part for a product.
In general, the LCD includes a large number of image pixels. When an image is to be displayed on the LCD, a graphic controller of the LCD will export the vertical synchronizing signal, horizontal synchronizing signal, and color signal to the liquid crystal timing controller. The liquid crystal timing controller the exports a control signal, according to the above signals, to the gate driver and exports the color signal to the data driver. As a result, the pixels are controlled in action.
Since the liquid crystal by itself cannot emit the light, it is necessary to include a back light source or an external light source to serve as the light source for displaying the image on the screen. In the case of using a light emitted diode (LED) to serve as a back light source, it usually needs a constant current to supply to each LED by a constant current source. Otherwise, it would easily occur that the LED is burnt down or the brightness is not uniform. The current conventional method is basically categorized into two manners. One is that each of the LED of the back light source is driven by coupling with a resistor in cascade. However, this manner does not improve efficiency or even reduce the efficiency. Another conventional method is directly using a constant current chip to provide a constant current to each LED. However, this constant current chip has to be designed externally. This would increase the use of space for the LCD driving circuit. Also and the fabrication cost is also increased.